Roughness is a key factor affecting the hydrodynamic characteristics of overland flow. In order to explore the hydraulic characteristics of overland flow under the influence of gradient roughness, using particle image velocimetry (PIV) to observe and analyze the velocity profile, turbulence intensity, Reynolds stress and wall shear stress of the overland flow under the three groups of flow rates. The results showed that: (1) The flow velocity decreased with the increase of roughness; the logarithmic formula of velocity distribution was obtained by fitting the dimensionless velocity. The increase of roughness was inversely proportional to the fitting constant A and proportional to the integral coefficient B. (2) The trend of streamwise turbulence intensity of gradient surface roughness was similar to that of smooth bed slope. The streamwise turbulence intensity decreased with the increase of relative water depth. With the increase of roughness, there was a nonsignificant difference in the intensity of streamwise turbulence. The turbulence intensity under the gradient rough bed was consistent with the Nezu empirical formula, and the flow rate was proportional to the empirical coefficient. (3) Under different flow rates, the Reynolds stress distribution of the graded rough bed was similar to that of the smooth bed. Under the influence of roughness, the maximum Reynolds stress appeared at y/H = 0.2~0.4. With the increase of roughness, the wall shear stress increased gradually. The synthesis showed that the method of increasing PIV resolution could be applied to the study of hydraulic characteristics of overland flow. Exploring the influence of gradient roughness on slope flow and exploring the hydrodynamic characteristics of slope flow provide new ideas for theoretical research of soil and water conservation.